AB - Vol. 17 No. 1 - Feature article

Cross-section through a colony of the bioeroding sponge Cliothosa aurivillii. Endolithic tissue is very soft and vulnerable, while exposed papillae are dense with spicules.

Photo: Christine Schönberg, scale 1 cm

NOTE

Schönberg CHL, Wisshak M

The perks of being endolithic

Why do endolithic bioeroders inhabit hard substrates when related species are free-living? Endolithic tissue that is contained within the substrate is protected against predators, parasites, diseases and adverse environmental conditions, and thus requires less maintenance than exposed parts, which are structurally re-enforced and may be chemically defended. Schönberg and Wisshak observed bioeroding sponges that were damaged during sampling and found that the soft endolithic tissue of Siphonodictyon mucosum only healed when it was shaded, and otherwise became diseased and disintegrated. Internal tissue of Cliothosa aurivillii initially healed, but then became infested with copepods feeding on it, apparently introducing the same disease and reversing the healing process. The endolithic lifestyle therefore makes these organisms susceptible to destruction when they become exposed.